[mercury-users] mode error #2

[Michael Day]

> > mode error: variable `Refs' has instantiatedness 
> > `bound((list:[]) ; list:'[|]'((pdf:object), list:list_skel((pdf:object))))',
> > 
> > expected instantiatedness was `list:list_skel((pdf:object))'.
> > 
> > Is this not the case, given the definition of list_skel?
> 
> Yes, I think you're right -- those two insts should be the same.

Here is a test case, note that it appears to be caused by a mistake on my
part, in that app2 is defined to take a list(T) and a T, when it should be
a list(object) and an object. Nonetheless, it's a fairly confusing error
message.

Michael

:- module foo.

:- interface.

:- import_module string, int, list.

:- type object ---> a ; b(func(string) = int).
:- inst object ---> a ; b(func(in) = out is det).

:- func foo(list(object)) = list(object).
:- mode foo(in(list_skel(object))) = out(list_skel(object)) is det.

:- implementation.

foo(Refs) = app2(Refs, a).

:- func app2(list(T), T) = list(T).
:- mode app2(in(list_skel(object)), in(object)) = out(list_skel(object)) is
det.

app2([], Y) = [Y].
app2([X|Xs], Y) = [X|app2(Xs,Y)].

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